Certain death? Of course not, that's absurd. I think you've got a very warped "pop-history" view of what the world was like long ago. Of course it depends entirely on when and where we're talking about (some periods in some places common folk practically never traveled, other times and places people were traveling all the time) but if we assume a time and place where traveling was common, a traveler could expect:

• Paved roads
• Plenty of places to stop and rest (even if there are no inns available, plenty of people are willing to take in travelers for a night, especially holy men on a pilgrimage)
• Few animals left who are willing to try preying on humans (they learned their lesson looooong ago)
• Infrequent disease (you're spending most of your time out in the open air with a small group of the same people, the only place for disease to come from is unclean water, which you know better than to drink outside of emergencies)

What part of these conditions reminds you of the tightly-packed, underfed, sedentary life of a slave being transported as cargo on a boat?